全文获取类型
收费全文 | 60680篇 |
免费 | 4070篇 |
国内免费 | 3991篇 |
专业分类
林业 | 6950篇 |
农学 | 2785篇 |
基础科学 | 3542篇 |
23578篇 | |
综合类 | 21311篇 |
农作物 | 1728篇 |
水产渔业 | 1072篇 |
畜牧兽医 | 2643篇 |
园艺 | 813篇 |
植物保护 | 4319篇 |
出版年
2024年 | 348篇 |
2023年 | 1446篇 |
2022年 | 1867篇 |
2021年 | 2058篇 |
2020年 | 2180篇 |
2019年 | 2496篇 |
2018年 | 1943篇 |
2017年 | 2815篇 |
2016年 | 3361篇 |
2015年 | 2408篇 |
2014年 | 3030篇 |
2013年 | 4143篇 |
2012年 | 5292篇 |
2011年 | 4303篇 |
2010年 | 3309篇 |
2009年 | 3481篇 |
2008年 | 3108篇 |
2007年 | 3347篇 |
2006年 | 2850篇 |
2005年 | 2506篇 |
2004年 | 1951篇 |
2003年 | 1683篇 |
2002年 | 1288篇 |
2001年 | 1231篇 |
2000年 | 1043篇 |
1999年 | 753篇 |
1998年 | 631篇 |
1997年 | 633篇 |
1996年 | 529篇 |
1995年 | 531篇 |
1994年 | 477篇 |
1993年 | 365篇 |
1992年 | 319篇 |
1991年 | 312篇 |
1990年 | 207篇 |
1989年 | 198篇 |
1988年 | 124篇 |
1987年 | 86篇 |
1986年 | 45篇 |
1985年 | 17篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1963年 | 1篇 |
1962年 | 5篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
991.
简述了国内外盐碱地的现状与分布,生物改良盐碱地的方法,已被科学家们所共识。我们利用碱茅属(Puccinelia Parl)植物改良盐碱地已取得重大进展。新育成的“吉农朝鲜碱茅”(P.chinampoesis Ohwi CV.“Jinong”)具有更加优良的性状和广泛的适应性。该品种将在“三北”地区的生态环境建设和盐碱地改良过程中发挥重要作用。 相似文献
992.
从网络安全管理平台建设的规划、定位、功能、结构、集成、运行维护等方面对国家林业局计算机网络的安全管理与策略进行了论述和探讨。 相似文献
993.
994.
995.
朱伯平 《四川畜牧兽医学院学报》2007,5(5):161-163
参与学生公寓的管理对于大学生勤工助学来说有着非常重要的意义,它不仅是大学生参加社会实践的一个重要方式,也是解决家庭经济困难学生问题的一种主要途径,同时在管理过程中也使学生实现了自我管理的目的。 相似文献
996.
Over the last few decades, several phenomena contributed to modify the structure and composition of the eastern North American forests. Along with forest management, disturbances such as insect defoliation, global environmental changes, acid deposition, and rising atmospheric CO2 concentrations, have been identified as phenomena that could affect forest structure and composition. Currently, there is very little quantitative information on the resulting effect of multiple disturbances on the main parameters of forest dynamics (growth, mortality, and recruitment). Using available data from the Quebec permanent sample plots network, we analyzed the ecological response of tree species populations to the combined effect of contemporary global environmental changes, disturbance regimes, and forest management practices over the last 30 years in southern Quebec. The results indicate that the main parameters of forest dynamics changed considerably over the last three decades. The last spruce budworm outbreak initiated a successional change in coniferous stands. The basal area of Abies balsamea and Picea glauca, the most abundant coniferous species, decreased by 29.7%, while pioneer species abundance increased. For late successional deciduous species, observed changes in forest dynamics appear to be mainly associated with global environmental changes rather than with natural disturbances or forest harvesting. The results indicate that inferring responses of tree population dynamics to global environmental changes can be very complex or even misleading considering the confounding effects of other disturbance agents. The results also suggest that the ecosystem-based management approach promoted by forest ecologists, aimed at maintaining landscape stand composition and structures similar to those characterizing natural environments, will not be easily achieved. Forest ecosystems are highly dynamic and disturbances other than tree harvesting appear to have been the major factors affecting their pattern of change over the last three decades. Forest managers should consider adaptive management approaches that will consider the contemporary evolution of forest ecosystems in a changing environment. 相似文献
997.
孔祥伟 《农业机械化与电气化》2009,(3):93-95
从改善电力网络功率分布、合理安排经济运行方式、加强农村电网改造等角度,论述了降低技术线损的措施;从制定线损指标计划、加强计量管理和抄收管理、建立管理线损考核制度和约束机制等方面入手,提出降低管理线损的具体措施。 相似文献
998.
999.
Abstract. The validity of the model described in Greenwood & Karpinets (1997) was tested against the results of single year, multi level K fertilizer experiments. Measurements of plant mass, %K in the plant and K activity ratio in soil had been made at harvest and at intervals during the growing season on spring wheat, summer cabbage and turnips. Reasonably good agreement was obtained between these measurements and simulated values when the two 'crop' parameters (defining the dependence of critical and maximum possible %K on plant mass) were adjusted for each crop. Also good agreement was generally obtained for plant weight and plant %K at harvest in less detailed experiments on 10 other crops. Values of the two 'crop' parameters for 12 of the crops were strongly correlated with one another suggesting that a single 'crop' parameter may be all that is required to define most inter-species differences in plant-K demand.
Simulations with the model indicate that, in central England, no response of 10 crops to K fertilizer would be likely on soils containing more than 170 mg of 1 M ammonium nitrate extractable-K/kg of soil and having clay contents of between 15 and 45%. Shortcomings of the model and opportunities for advance are discussed.
A simplified version of the model runs on the Internet at: http://www.qpais.co.uk/moda-djg/potass.htm 相似文献
Simulations with the model indicate that, in central England, no response of 10 crops to K fertilizer would be likely on soils containing more than 170 mg of 1 M ammonium nitrate extractable-K/kg of soil and having clay contents of between 15 and 45%. Shortcomings of the model and opportunities for advance are discussed.
A simplified version of the model runs on the Internet at: http://www.qpais.co.uk/moda-djg/potass.htm 相似文献
1000.
家庭蚕桑适度规模经营的实践探索 总被引:1,自引:0,他引:1
推地蚕桑适度规模经营是提高蚕桑生产经济效益的一项主要途径。海宁市对蚕桑适度规模经营进行了试点实践和调查,并就提出该课题的依据,可能性,典型蚕户的经营分析,适度规模经营的指标,优缺点进行了有益探讨。 相似文献